ANNEALING TEMPERATURE-DEPENDENCE OF MGO SUBSTRATES ON THE QUALITY OF YBA2CU3OX FILMS PREPARED BY PULSED-LASER ABLATION

The effect of annealing on a MgO substrate was systematically investig ated, varying the annealing temperature, for preparation of high-quali ty YBa2Cu3Ox (YBCO) films by pulsed laser ablation. X-ray photoelectro n spectroscopy (XPS) and atomic force microscopy (AFM) were carried ou t for characterization of the MgO substrate and X-ray diffraction (XRD ) measurement, including theta-2 theta scan, omega-scan (rocking curve ) and phi-scan, and electrical measurement were carried out for charac terization of YBCO films. Thermal annealing of MgO above 1000 degrees C in oxygen ambient was found to give rise to a great improvement of t he crystallinity and the reproducibility of crystal orientation of YBC O films, while it was also found to induce Ca segregation on the surfa ce of MgO and reduce the oxygen content of YBCO films. Annealing below 1000 degrees C causes no outstanding improvement in the crystal struc ture of YBCO. On the MgO substrate annealed at 1200 degrees C c-axis-o riented YBCO film was found to reproducibly show a full width at half- maximum (FWHM) of the rocking curve of 0.3 degrees, an FWHM of (005) d iffraction of 0.1 degrees, an epitaxial relation without in-plane miso rientation, a critical zero temperature of 89 K, and a critical curren t density of 10(6) A/cm(2) at 77.4 K and zero field.